1. Field of the Invention
The present invention generally relates to an isolator mount. Specifically, the invention is comprised of an alloy or rare earth material integrated within an isolation mechanism so as to impede both shock and vibration. The invention includes a semi-passive mode for harsh environments and an active mode for benign environments. Manufacturing processes are described facilitating the integration of alloys and rare earth materials within a plastic, composite, and metal.
2. Related Arts
Naval ships employ a wide variety of isolator mounts to impede acoustic transmissions and to protect sensitive equipment from shock and vibration. Presently, isolator mounts are specifically designed for a limited range of shock and vibration conditions. Consequently, a variety of mounts are required to satisfy a wide range of mechanical load conditions. Furthermore, energy dissipation mechanisms employed within such devices quickly degrade their performance thereby requiring constant replacement. Specifically, passive mounts comprised of rubber and metal rapidly lose their damping capacity. Consequently, isolator mounts are often used well beyond their effective lifetime thereby compromising the integrity and performance of shipboard systems.
Active isolator mounts with integrated electronics increase the range of shocks and vibrations effectively isolated. However, active mounts are generally less durable and sensitive to environmental conditions. Wires externally attached to such devices are susceptible to breakage. Electronics within such devices are susceptible to the very shocks and vibrations dissipated. And electronics within such devices are susceptible to damage by saltwater, ozone, and oil.
Low-frequency shocks, typically in the range of 3 to 10 Hz, and vibrations, typically in the range of 5 to 30 Hz, exclude many conventional passive and active damping devices. For example, the effectiveness of viscoelastic damping increases with frequency and thereby of limited utility at low frequencies. Passive damping with piezoelectric or electrostrictive devices, also known as direct effect damping, is not particularly useful at low bandwidths since damping is dependent upon hysteresis loops and elastic-mechanical-to-electrical energy coupling. Coupling coefficients are generally poor and total loss is insignificant at the lower dynamic range.
Piezo-polymers are better direct coupling materials than piezoceramics and electrostrictors, therefore applicable to piezo-passive damping devices. In a passive-mode device, a generalized matched impedance circuit couples to the active ferroelectric materials transferring elastic energy as heat. In a semi-active mode, the circuit is variably tunable. However, force and strength-stiffness characteristics preclude the use of ferroelectric polymers such as PVDF and urethane as active devices.
The present invention reveals a method of manufacture for a thermoplastic mount incorporating an externally constrained viscoelastic damping layer and/or ferromagnetoelastic damping laminate. These treatments are individually applied or applied in combination to commercially available or other thermoplastic material mounts. The disadvantage of the laminate process is some small loss in isolation (<5%) with a corresponding large increase in wide band damping (>40%) to nearly dc.
The present invention is fabricated by a non-conventional method of extrusion enabling the netshape production of thermoplastic, including formulations in the Hytrel® family, damping elements about an energy dissipating material. The described method not only introduces a more reliable method for fabrication of mounts such as commercial C-mounts using extrusion (see FIG. 12), but enables the present invention to mimic enhanced performance of ferromagnetoelastic damping laminate in a full composite construction, whereby damping alloys are introduced as particulates or fibers during the pre-mixing process. Although, the present invention could be similarly applied to injection molding techniques, the further advantage of the invention of extrusion in contrast to injection, is that with extrusion the ferromagnetoelastic materials can be aligned into virtual chains which is known to increase damping effectiveness.
What is required is an isolator mount possessing both soft-damping for small disturbance excitations and stiffness to mitigate large shocks. The invention achieves a high level of damping for both shock and vibration, yet retains static stiffness characteristics. The invention should function over a wide range of temperature and load conditions. The invention should facilitate quasi-static tuning for adaptive passive damping.